The driver of the future engine technology will be the reduction of the CO2 emissions which is strictly related to fuel consumption saving. Recent regulations on pollutant emissions and greenhouse gases require a technological effort on engine efficiency which can be made with a different set of options. It is important to consider those ones that have lower costs and a suitable ratio between CO2 reduction and cost. Relevant importance is, so, assumed by a revision of the engine cooling system, which remained substantially unchanged for several years or decades. If the engine and vehicle thermal needs are considered in a whole way, the cooling system can be rearranged realizing the integration of conventional thermal needs (engine, oil and EGR cooling) with unconventional ones (cabin conditioning, charge air cooling) realizing benefits in terms of engine efficiency and comfort. In this paper, a mathematical model of an internal combustion engine is presented. It is a lumped parameter model, physically consistent and it is used to appraise the performances of conventional and unconventional engine cooling systems and the integration in it of vehicle thermal needs. In particular, a double cooling circuit has been considered, with two different temperature levels, that allows important improvements in terms of engine warm up, fuel consumption saving and air boosting. The model has been applied to an existing engine whose experimental characterization was done concerning the heat rejection toward the cooling fluid. On this engine, a double circuit at two temperature levels has been proposed, according to a layout which redistribute in an optimal way the engine and vehicle thermal requirements. (C) 2013 Elsevier Ltd. All rights reserved.